Not to imply all authors are mad, but many of us stash away plot ideas for a rainy day. Sometimes it's a cookie jar stuffed with wild scratchings and other times a more ordered folder on our laptop. This stash is the box of chocolates we dip into when it's that time to sit down and start writing a brand new book.
My ideas generally come as characters rather than plots, I don't do much plotting up front from either way. I have a clear idea of the main characters, what drives them and, usually, they come to me in a turning-point scene. At this point, I have no idea whether this scene will start the story or be somewhere down the line. So, instead of a Plot Hat, I have a Scene Hat. I write a couple of pages of the scene (in some cases, up to a full chapter) to record the flavour of my characters, their speech, taste, feel, scent and attitude. As this scene is usually a turning-point, or at least vital to the story, recording this scene also lays the foundation for the story even though I don't jot down anything of the surrounding plot. Sometimes this changes between the initial idea and what I end up writing, sometimes I don't remember what I originally had in mind but the characters I've written speak to me and take me into their world regardless, and their story unfolds.
Why am I rambling about this now? LOL, I've just finished my current work in progress and it's that time again for me. I get to dive into my hat and see what characters and scene I catch for the start of a brand new journey